1. Technical Field
The present invention relates to an image projection apparatus.
2. Background Art
Some image projection apparatuses include a box-shaped enclosing unit such as a mirror box that retains optical parts such as a co-axial lens and a curved mirror and has an opening on a top face of the enclosing unit used for exiting a projection image. Further, the image projection apparatuses may include a shutter to cover the opening of the mirror box, an air supply unit such as an air supply fan to inflow air into the mirror box.
The shutter closes the opening when a projection image is not projected to a screen, with which dust intrusion into the mirror box through the opening when the image projection apparatus is stopped can be prevented. When a projection image is being projected onto the screen, the air supply fan inflows air into the mirror box, with which an internal pressure of the mirror box becomes higher than an external pressure of the mirror box, and the shutter is opened to project an image onto the screen through the opening. When the projection image is projected onto the screen, an airflow flowing from the internal space of the mirror box to the outside of the mirror box is generated at the opening, with which dust intrusion from the opening can be suppressed.
However, in this image projection apparatus disclosed in JP-4018459-B (JP-2004-12750-A), air supplied from the air supply fan directly flows to the opening, further, an area of the opening for exiting the projection image is greater than an area of an opening for discharging air from the air supply fan. Therefore, when an image is being projected by opening the shutter, air supplied into the mirror box from the air supply fan may not remain in the mirror box effectively but may be exhausted from the opening. Therefore, it becomes difficult to maintain the internal pressure of the mirror box higher than the external pressure outside the mirror box, and resultantly, an airflow flowing into the mirror box from the outside of the mirror box may occur at an edge of the opening, and dust intrusion into the mirror box through the opening may occur. The dust intruded through the opening may adhere on optical parts, with which the projection image quality may deteriorate.